Our preliminary observations suggest that athletic training, specifically swimming, before the onset of puberty is associated with a delay in the onset of menarche (primary amenorrhea). Furthermore, there appears to be a greater incidence of menstrual irregularity in athletes with a later age of menarche. Primary amenorrhea of athletic origin may also be associated with the attainment of a greater adult stature and our evidence suggests that the delay in menarche may be due to the inability of subjects to achieve a critical body fatness. However, since changes in menstruation take place before any alteration in body composition, post-menarchal menstrual irregularity and secondary amenorrhea do not appear to be related to the maintenance of a critical level of body fatness but rather to factors associated with exercise itself. The proposed project will examine the impact of long distance running initiated either before or after menarche on subsequent growth and menstrual function. Three groups of college-age girls, each group consisting of 100 subjects will be studied: a) a non-athletes, b) long distance runners who began training before menarche, c) long distance runners who began training after menarche. Their menstrual status, anthropometric characteristics of growth, and body fatness will be compared. This study is meant to establish whether or not prepubertal intense physical activity could delay the onset of puberty which may lead to a greater incidence of later menstrual dysfunction as well as alteration of specific characteristics of growth. Since it is suggested that exercise itself may induce amenorrhea. The project will also examine the hormonal profiles of four groups of women; a) non-athletes, b) athletes with regular menstrual cycles, c) athletes with primary amenorrhea, and d) athletes with secondary amenorrhea. The hormones to be measured will be luteinizing hormone, follicle stimulating hormone, estradiol and progesterone, and the aim will be to correlate the hormonal profiles with menstrual function. In other experiments the presence or absence or absence of pulsatile release of gonadotropins and prolactin will be examined in order to further define their hormonal status. Finally, the hypothesis will be tested that exercise specifically induces hyperprolactinemia, one of the most common causes of amenorrhea in women, by meusuring the serum prolactin and cortisol response to graded levels of exercise.